1. Field of the Invention
The invention relates to screening of electrolytic capacitors. It can be used for screening out unreliable parts from the general population of the capacitors as well as for screening for most reliable capacitors for special applications such as medical and military applications. It can be also used for comparison of different materials and manufacturing techniques.
2. Background and Prior Art
Accelerated aging at elevated voltage and temperature, surge tests, re-flow test, etc. are incorporated in manufacturing of electrolytic capacitors to display hidden defects in the dielectric and to screen for non-reliable parts. The problem with these techniques is that they cannot guarantee exclusion of all the non-reliable parts and, when intensified, can deteriorate performance and reliability of the general population of the capacitors as a result of the testing.
U.S. Pat. No. 5,882,719 issued Mar. 16, 1999 to R. Creasi is exemplary of the prior art. This patent describes a test that provides reliability indication at early stages of the manufacturing of solid Ta capacitors. This test comprises testing in a wet cell Ta capacitors partially impregnated with solid electrolyte using static voltage exceeding working voltage (WV) or in gradually increased (sweep) voltage exceeding WV. In both cases the applied voltage results in electrical breakdown of the dielectric in poor capacitors, while good capacitors survive the test and continue through the manufacturing process.